1. Field of the Invention
The present invention relates to a wet-type multi-plate frictional engagement apparatus using wet-type friction material. More specifically, the present invention relates to a wet-type multi-plate frictional engagement apparatus having a plurality of clutch plates which is preferably used in an automatic transmission for a car, and the like, and in a transmission for a motorcycle, and the like.
2. Related Background Art
An example of the conventional frictional engagement apparatus is shown in FIG. 1. This frictional engagement apparatus consists of: a shaft barrel member 14 fixed to a transmission case (not shown); a clutch drum 1 rotatably supported by said shaft barrel member 14; and a clutch hub 3 fixed to another clutch drum (not shown). The clutch drum 1 has an outer drum 8 and an inner drum 9, which is built in the outer drum 8 and fixed to the inner peripheral surface of the outer drum 8 by spot welding, or the like. As for the apparatus shown in FIG. 1, the inner drum 9 is fixed to the outer drum 8 by spot welding. Clutch plates are steel plates on which wet-type friction material is attached. Passive clutch plates 2 are held by the inner drum 1 of the clutch drum 9, while drive clutch plates 4 are held by the outer periphery of the clutch hub 3. These clutch plates are arranged alternately so that the surfaces on which frictional material is attached face the metal surfaces. Reference numeral 8a denotes an oil supply hole.
In this construction, when a piston 6 presses the passive clutch plates 2 and the drive clutch plates 4, each plate slides frictionally while nipped between the piston 6 and a stopper member 9a fixed to the inner drum 9.
FIG. 2 shows partially broken cross sections of the outer drum 8 and the inner drum 9, which are cut along the line A--A in FIG. 1. As shown in FIG. 2, the inner drum 9 is fixed to the inner peripheral surface of the cylindrical outer drum 8. The inner drum 9 consists of cylindrical portions 11 and a plurality of spline grooves or splines 10. The splines 10 are formed at predetermined positions on the circumference of the inner drum 9 so as to project outward in radial directions. The splines 10 have a certain length in the direction of the axis of the inner drum 9 so as to carry a plurality of clutch plates. Because the front edges of the splines 10 are fixed to the inner peripheral surface 12 of the outer drum 8 by welding, or the like, the inner drum 9 is rotated integrally with the outer drum 8.
A plurality of the splines 10 formed on the circumference of the inner drum 9 are arranged symmetrically with respect to a certain diameter or symmetrically with respect to the center of the circular cross-section. These splines 10 engage with respective projecting portions of the clutch plates. The projecting portions project outward in the radial directions and have shape corresponding to the cross sections of the splines 10. Thus, the clutch plates are mounted in the inner drum 9. When the clutch plates are assembled into the clutch drum, the surfaces on which frictional material is attached are distinguished from the metal surfaces, for example, by observing them visually so that the surfaces on which frictional material is attached are faced with the metal surfaces. In order words, neither frictional surfaces nor metal surfaces are faced with each other.
As for the above-mentioned conventional friction engagement apparatus, since the surfaces on which frictional material is attached are distinguished from the metal surfaces by visually observing them, touching them, or the like when the clutch plates are put in the clutch drum, the clutch plates may be assembled inversely. Once they are assembled inversely, there is no way to check the arrangement after assembling.
In case some clutch plates of the above device are assembled inversely (backwards), frictional surfaces may face and engage each other and metal surfaces may face and engage each other. In such case, not only does capacity of driving torque decrease, but the frictional material may be burned and damaged. In the worst case, it becomes impossible for a car to move.
In order to meet concerns regarding energy and the environment, a frictional engagement apparatus is required not only to be small and lightweight, but also to have excellent durability, especially against heat. However, the above-described structure is subject to temperature differences between the frictionally engaged surfaces of the drive clutch plates and those of the passive clutch plates, because heat capacity of the clutch drum is different from that of the clutch hub. As a result, the frictional material on the passive clutch plates and the drive clutch plates may suffer from abnormal abrasion, and the durability of the frictional engagement apparatus varies, depending on working conditions.
Therefore, a first object of the present invention is to provide a wet-type multi-plate frictional engagement apparatus employing metal clutch plates having wet-type frictional material only on one side, wherein the shape, or the like, of the splines formed on either the outer periphery or the inner periphery of each metal plate is made to be asymmetrical and the shape of the splines of the clutch drum or the clutch hub is made to correspond to that of the splines of each clutch plate so that the clutch plates cannot be installed backwards and the surfaces on which wet-type frictional material is attached are always faced with the metal surfaces.
A second object of the present invention is to provide a wet-type multi-plate frictional engagement apparatus which can uniform abrasion loss of the drive clutch plates and that of the passive clutch plates and which can prevent variation in durability, and thereby improve the overall durability, by thickening the splines of the clutch plates. Thus, the heat capacity of the clutch drum or that of the clutch hub does not have to be varied, that is, materials employed or the design need not be changed.